Even though the GFUI is not showing you the full bed, it is showing the full usable area of the bed. For examples of what the camera sees, take a look at this post:
So, for now we need to design within these limits.
As a suggestion to help work around this, try ignoring the top three pieces and cut the bottom ones. Then shift the material down and cut the top ones. Not optimal, I know, but should be able to get your design made without wasting material.